PCT application WO 91/06629, published 16 May 1991 and assigned to Gilead Sciences Inc., describes modified oligomers and derivatives thereof which contain nucleotide sequences useful in binding a biological moiety wherein the modification comprises substitution for one or more linkages between individual nucleotide residues, a linkage of the formula --YCX.sub.2 Y--, wherein each Y is independently O or S and wherein each X is independently chosen and is a stabilizing substituent. This application, the disclosure of which is incorporated herein by reference, describes these oligomers and their derivatives, and the manner in which they are useful in a variety of contexts by virtue of the ability of the oligomers to bind various biological moieties. These oligomers are therefore useful, for example, as diagnostic agents.